This invention relates to interchangeable component identification systems and more particularly to an electronic system for indicating which one of a plurality of interchangeable probes or work elements is interconnected with an overhead arm assembly.
The invention is particularly applicable for use with medical ultrasonic diagnostic apparatus and will be described with particular reference thereto. However, it will be appreciated that the invention has broader applications in other fields in which work elements are regularly interchanged.
In ultrasonic medical diagnostics, images of internal areas of a patient are obtained by transmitting ultrasonic energy into the patient and monitoring the ultrasonic echoes. A planar slice of the patient is most commonly examined. The examination is typically accomplished by utilizing a single probe element which both transmits ultrasonic energy and receives the echoes. By monitoring the position and orientation of the probe as it is moved to various points along the line of intersection between the planar slice and the surface or body of the patient, signal processing equipment can transform the position data and echoes into a representation of the examined planar slice. An example of such processing equipment is shown in U.S. Pat. No. 3,036,390.
The structural characteristics of the transducers determine the application to which they are best suited. Accordingly, it is advantageous for the operator to change transducer heads for different types of examinations. For example, transducers with higher or lower sensitivity may be desired. As another example, the diameter of the transducer is a determining factor of the depth within the patient at which ultrasonic waves are most precisely focused, i.e. focal length.
Providing an operator with a plurality of interchangeable transducer heads leads to difficulty in identifying the transducers. This difficulty is compounded when the need for identification arises during a scan when the transducer head is in a relatively inaccessible position and being moved or after a scan when viewing a photograph of the ultrasonic image.
The ultrasonic probe is normally carried by an arm assembly defined by a plurality of movable, jointed arms. These arms are constrained to movement within a single plane, i.e., the plane of the patient slice which is to be examined. Prior arm assemblies have generally comprised a plurality of pivotally interconnected arms, such as is shown in U.S. Pat. No. 3,924,452, a plurality of linearly, slideably jointed arms, such as is shown in U.S. Pat. No. 3,036,390 or a combination of these two arrangements. The designs of these and other prior arm assemblies have been such that there were problems in accurately selecting the plane of examination. Some prior assemblies were also lacking in adjustment flexibility and required movement of the patient for purposes of changing the plane of examination.
To determine the position and angular orientation of the transducer probe at the end of the arm assembly, conventionally each pivot between the arms is associated with a variable resistor or potentiometer. The variable resistor is interconnected with the arms such that as the arms pivot relative to each other the resistance changes. By monitoring the resistance or change in a voltage applied across the variable resistor, the orientation of the probe may be determined. See "Ultrasonic Contact Scanner for Diagnostic Application", J. H. Holmes et al., American Journal of Medical Electronics 1965.
Interconnecting the potentiometer with the arms has been accomplished with a series of belts and pulleys, see for example, U.S. Pat. No. 3,924,452. But such a system is bulky and subject to belt slippage and breakage. The interconnected has also been tried by locating the potentiometer at the pivot with the shaft of the variable resistor forming part of the pivot mechanism. This interconnection, however, places excessive forces on the shaft and bearing of the variable resistor causing frequent variable resistor failure.
In practical application, doctors often wish to obtain and view more than one planar slice of a patient. These plural slices are most reliably diagnosed if they are parallel and spaced apart by known increments. In prior arm assemblies, especially those which required patient movement for changing the plane of examination, movement to parallel planes was usually arduous and imprecise. Even in the selection of an initial or first plane, alignment of the plane of interest in the patient and the scan plane of the arm was often haphazard and imprecise.
Another problem encountered with prior arm assemblies is that they have been awkward to operate. In some prior assemblies, the scan arms have not been counterweighted or if counterweighted, they have been done so in a crude and inaccurate manner. Often the arms have been constructed of lightweight materials and without proper counterweighting which required the operator to exert different amounts of force to produce the same scanning movement in different portions of the scan plane. This problem resulted in undesired degradation of the visual image being produced.
The present invention contemplates new and improved apparatus which overcomes all of the above referred to problems and others and provides an overhead arm and scanning assembly which is flexible, easy to use, and precisely oriented.